Originally Posted by glye

Sheldon Brown says Shimano Nexus / Alfine sprockets will work with either 1/8" or 3/32" chains, so free choice. But the chainring may not because of its chainguards, so 3/32 is the safest bet I think. meaning afaik 7- 8- or 9-speed chain, or a dedicated 1-speed 3/32 chain. Kindly don't sue me if I'm wrong.
https://www.sheldonbrown.com/harris/shimano-nexus.html

Originally Posted by glye

Thanks for sharing. So the single speed chain you used is 1/8" wide, then? Single speed chains also exist in 3/32" width, which is about the same width as an 8/9-speed chain, so it should not rub anything. But I guess the difference between that and an actual 9-speed is small, and they will work equally well in practice. Perhaps the single speed 3/32" is a little stiffer side-to-side and less likely to derail.